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package java.awt;

import java.awt.peer.ComponentPeer;


/**
 * A FocusTraversalPolicy that determines traversal order based on the order
 * of child Components in a Container. From a particular focus cycle root, the
 * policy makes a pre-order traversal of the Component hierarchy, and traverses
 * a Container's children according to the ordering of the array returned by
 * <code>Container.getComponents()</code>. Portions of the hierarchy that are
 * not visible and displayable will not be searched.
 * <p>
 * If client code has explicitly set the focusability of a Component by either
 * overriding <code>Component.isFocusTraversable()</code> or
 * <code>Component.isFocusable()</code>, or by calling
 * <code>Component.setFocusable()</code>, then a DefaultFocusTraversalPolicy
 * behaves exactly like a ContainerOrderFocusTraversalPolicy. If, however, the
 * Component is relying on default focusability, then a
 * DefaultFocusTraversalPolicy will reject all Components with non-focusable
 * peers. This is the default FocusTraversalPolicy for all AWT Containers.
 * <p>
 * The focusability of a peer is implementation-dependent. Sun recommends that
 * all implementations for a particular native platform construct peers with
 * the same focusability. The recommendations for Windows and Unix are that
 * Canvases, Labels, Panels, Scrollbars, ScrollPanes, Windows, and lightweight
 * Components have non-focusable peers, and all other Components have focusable
 * peers. These recommendations are used in the Sun AWT implementations. Note
 * that the focusability of a Component's peer is different from, and does not
 * impact, the focusability of the Component itself.
 * <p>
 * Please see
 * <a href="https://docs.oracle.com/javase/tutorial/uiswing/misc/focus.html">
 * How to Use the Focus Subsystem</a>,
 * a section in <em>The Java Tutorial</em>, and the
 * <a href="../../java/awt/doc-files/FocusSpec.html">Focus Specification</a>
 * for more information.
 *
 * @author David Mendenhall
 * @see Container#getComponents
 * @see Component#isFocusable
 * @see Component#setFocusable
 * @since 1.4
 */
public class DefaultFocusTraversalPolicy
    extends ContainerOrderFocusTraversalPolicy {

  /*
   * serialVersionUID
   */
  private static final long serialVersionUID = 8876966522510157497L;

  /**
   * Determines whether a Component is an acceptable choice as the new
   * focus owner. The Component must be visible, displayable, and enabled
   * to be accepted. If client code has explicitly set the focusability
   * of the Component by either overriding
   * <code>Component.isFocusTraversable()</code> or
   * <code>Component.isFocusable()</code>, or by calling
   * <code>Component.setFocusable()</code>, then the Component will be
   * accepted if and only if it is focusable. If, however, the Component is
   * relying on default focusability, then all Canvases, Labels, Panels,
   * Scrollbars, ScrollPanes, Windows, and lightweight Components will be
   * rejected.
   *
   * @param aComponent the Component whose fitness as a focus owner is to be tested
   * @return <code>true</code> if aComponent meets the above requirements; <code>false</code>
   * otherwise
   */
  protected boolean accept(Component aComponent) {
    if (!(aComponent.isVisible() && aComponent.isDisplayable() &&
        aComponent.isEnabled())) {
      return false;
    }

    // Verify that the Component is recursively enabled. Disabling a
    // heavyweight Container disables its children, whereas disabling
    // a lightweight Container does not.
    if (!(aComponent instanceof Window)) {
      for (Container enableTest = aComponent.getParent();
          enableTest != null;
          enableTest = enableTest.getParent()) {
        if (!(enableTest.isEnabled() || enableTest.isLightweight())) {
          return false;
        }
        if (enableTest instanceof Window) {
          break;
        }
      }
    }

    boolean focusable = aComponent.isFocusable();
    if (aComponent.isFocusTraversableOverridden()) {
      return focusable;
    }

    ComponentPeer peer = aComponent.getPeer();
    return (peer != null && peer.isFocusable());
  }
}
